End effector

ABSTRACT

A quill style drilling/milling end effector with high tool positioning accuracy, a pressure foot with fast response in force and displacement feedback, and with automatic mounting and dismounting, normality sensing, and through the tool coolant delivery.

FIELD OF THE INVENTION

The invention relates to machine tools and, more particularly, to endeffectors typically used with robots.

RELATED ART

Traditionally, the machining or other like work on large bodies orassemblies has been accomplished with even larger equipment that has abed for receiving or holding the body and for supporting and drivingtools at a point or points in the space surrounding the body. In morerecent times, industrial robots have been available to position andsupport tools for operation on large bodies. Conventional machines,whether a large monument type, or a gantry type have limitations on theaccuracy by which they can position and hold a tool with respect to thebody being machined or otherwise operated on. As technology hasadvanced, there has developed a need for precision positioning oftooling or other instrumentalities that exceeds the capability ofconventional equipment to machine large parts, bodies or assemblies. Thesize and mass of the machinery as well as temperature conditions arefactors that contribute to making the task of holding accurate machiningtolerances difficult if not impractical. Further, active joints,bearings, slides, couplings, and the like can introduce lash, again,making precise positioning of tooling elements difficult.

Applications of a robotic end effector can benefit from or require apressure foot that first engages the work before a tool is deployed. Itcan be desirable to automatically remove a pressure foot from an endeffector, for example, when its function is not required, when automatictool changes require removal of the pressure foot, or when a differentpressure foot is needed.

Some applications require that the end effector extend a tool towardsthe workpiece in a direction that is precisely normal to the surface tobe worked. Many applications can require or benefit from coolantdelivery through the tool. Weight of an end effector is a disadvantagein robotic applications since the size of a robot is typically dependenton the weight it must support and, generally, the larger the robot, theslower and less accurate it is. It is, therefore, desirable that theelements and instrumentalities employed to obtain these and otherbeneficial features allow an end effector to be compact and low in mass.

SUMMARY OF THE INVENTION

The invention provides an improved quill style drilling/milling endeffector with high tool positioning accuracy, a pressure foot with fastresponse in force and displacement feedback and with automatic mountingand dismounting, normality sensing, and through the tool coolantdelivery. Accurate tool positioning is accomplished with a micropositioner that is interposed between the end effector carrier,typically a robot arm or a gantry machine, and the tool spindle. Themicro positioner can be operated after the macro positioning carrier haslocated the tool spindle as close as practical to the site at which workis to be performed. This arrangement enables the micro positioner toeliminate imprecision in the carrier positioning of the end effectorrelative to the specified machining location.

In a preferred arrangement, the micro positioner comprises two slidesarranged with axes perpendicular to one another and perpendicular to thespindle axis of the end effector, thus affording two additionalpositioning axii to the host robot or other carrier. The slides arearranged on-center with the drilling/milling axis of the end effector,thereby avoiding excessive eccentric loading of the end effector andsimplifying position control.

The disclosed micropositioning system works with a pressure foot devicethat effectively couples and stabilizes the robot arm relative to theworkpiece before the micro positioner is operated. This arrangementenables the micro positioner to reliably eliminate errors in the robotpositioning of the end effector relative to the desired machininglocation.

The disclosed end effector accessories are uniquely developed andarranged for a quill style end effector and achieve benefits that arenot readily obtainable with other drilling/milling end effector designs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front isometric view of an end effector unit embodyingaspects of the invention;

FIG. 2 is a rear isometric view of the end effector unit;

FIG. 3 is a fragmentary top view of the end effector unit showingdetails of the micro positioner;

FIG. 4 is a fragmentary side view of the end effector unit showing themicro positioner;

FIG. 5 is a view of a tool changer with the master and tool sidesseparated;

FIG. 6 is a cross-sectional view of a ball coupling of the tool changerof FIG. 5;

FIG. 7 is a front perspective view of a second embodiment of an endeffector unit;

FIG. 8 is a diagram illustrating the relative positions of certainelements of the end effector of FIG. 7;

FIG. 9 is a longitudinal cross-sectional view of the spindle area of theend effector of FIG. 7;

FIG. 9A is an enlarged cross-sectional view of the rear end of the endeffector of FIG. 7; and

FIG. 9B is an enlarged cross-sectional view of the spindle end of theend effector of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2, a drilling/milling end effector unit 10is adapted to be supported by an industrial robot through a tool side 11of a tool changer. The illustrated end effector 10 is similar inconstruction to that disclosed in U.S. Pat. No. 7,547,169, thedisclosure of which is incorporated herein by reference. The endeffector unit 10 has a spindle indicated in phantom at 12 rotatableabout an axis 15. The forward end of the spindle 12 is surrounded by ahollow nose or cone 13.

An electrically driven servomotor 16 at the top of the unit 10 drives anaxial quill feed through a belt within a housing 17. Anotherelectrically operated servomotor 18 at the bottom of the unit 10 drivesthe spindle 12 through an associated belt. The end effector unit 10includes a frame or pressure bridge 19, U-shaped in plan view, to whichthe tool changer 11 is attached and which supports the remainingcomponents of the unit. The tool changer tool side 11, which can be acommercially available unit such as manufactured by ATI IndustrialAutomation, Inc. of Apex, N.C. 27539, USA, is fixed on a rear face ofthe pressure bridge 19. The tool side 11 is arranged to automaticallycouple with a complementary master side of a tool changer fixed to theend of an arm of an industrial robot such as manufactured by KUKARoboter GmbH. The changer tool side 11, in addition to automaticallycoupling the pressure bridge 19 to a robot arm, provides for utilitiesincluding electrical signals, air pressure, and coolant to be suppliedto the end effector unit 10. A vacuum tube 21 runs between the interiorof the spindle nose 13 and the changer tool side 11 for collectingmachining chips and debris.

The spindle nose 13 is removably attached to a plate or pressure foot 23by a tool changer 51. The tool changer 51 is shown in greater detail inFIGS. 5 and 6 and discussed below. The pressure foot plate 23 is carriedon four guide rods 26 distributed about and parallel to the spindle axis15. The guide rods 26 slide in linear bearings 27 fixed to the front ofthe pressure bridge frame 19 enabling the pressure foot 23 and spindlenose 13 to move in the axial direction of the spindle 15 relative to theframe. An associated electrically operated servomotor 31 fixed on theframe 19 rotates a helical screw shaft 32 in a ball nut 33 fixed on theplate 23 to positively mechanically extend or retract the plate andspindle nose 13. The servomotor 31, operated by the end effectorcontroller, feeds back electrical signals through the tool changerrepresented by the tool side 11 to the end effector controller thatindicate the angular displacement of the motor 31 from a referenceposition and the torque being applied by the motor. These signals areessentially instantaneous indications of the extension of the spindlenose 13 and the force being applied by the spindle nose. The speed orresponse of these signals can be used by the end effector controller toachieve a fast machine cycle time. Moreover, the spindle nose extensionor displacement data supplied by the servomotor 31 can be compared withthat provided by a linear transducer connected between the pressurebridge 19 and the pressure foot plate 23 to detect an error in either ofthese signals.

Mounted on an inner face of a rear wall 36 of the pressure bridge frame19 are two slides 37, 38. Each slide 37, 38 has a table 39, 40 capableof moving in an associated plane parallel to the wall 36 andperpendicular to the spindle axis 15. A first slide 37 moves vertically,in the orientation of the unit 10 shown in FIGS. 1 and 2, relative tothe pressure bridge frame 19 on linear bearings 41 supported directly onthe wall 36. Precision displacement of the slide 37 is produced by anassociated electrically operated servomotor 42 mounted on the frame 19.The second slide 38 is mounted on the first slide 37 and movesvertically with the first slide and horizontally relative to the firstslide and the frame 19 on linear bearings 43 carried on the first slidetable 39. Precision displacement of the second slide 38 is produced byan associated electrically operated servomotor 44 mounted on the firstslide 37.

Together, the slides 37, 38 and actuators or servomotors 42, 44 comprisea two-axis micro positioner 45 that can adjust the spindle 12 along twomutually perpendicular axiis that are each perpendicular to the spindleaxis 15. Each of the slides 37, 38 is capable of moving a total of, forexample, 1″ along its respective axis. Ideally, a spindle housing 46fixed to the slide table 40 is located so that when each of the slides37, 38 is in its center position, the spindle axis 15 is coincident withthese center positions. Together, the slides 37, 38 and associatedservomotors 42, 44 provide adjustment in any direction in a planeperpendicular to the spindle axis 15. While the displacement availableat the slides 37, 38 is limited, this displacement provides anadjustability much greater than the positioning accuracy of a typicalrobot sized to handle the weight of the end effector 10.

More specifically, the end effector unit 10 can be mounted on the end ofa robot arm so that the end effector can be coarsely brought intoworking position relative to a workpiece. The workpiece can berelatively large in comparison to the unit 10, being, for example, atleast several times as large. A robot large and strong enough to supportthe unit 10 throughout a major part of the space surrounding a largeworkpiece may have limited accuracy in positioning the unit, and suchaccuracy may not be sufficiently precise to satisfy the manufacturingspecifications of the large workpiece. A robot of a size adequate tohandle the end effector unit may have, for example, a positionalaccuracy of about ±0.020″. The micro positioner 45 of the inventionovercomes this positioning limitation of a robot by precisely locatingthe end effector unit 10 relative to a workpiece within, for example,about ±0.0002″ in a plane generally parallel to the workpiece surface.Various techniques, including use of an optical target, can be used bythe robot and end effector unit controller or controllers to operate themicro positioner 45 to precisely locate the spindle axis 15 in spacerelative to the workpiece. When a controller determines a positioningerror smaller than that ordinarily taken up by a robot or othermanipulator of the end effector unit 10, the controller can energizeeither or both of the micro positioner servomotors 42, 44 to preciselyalign the spindle axis 15 with the work site. During the time that apositioning error is found and while the micro positioner 45 is beingoperated, the pressure foot plate 23 operating through the spindle nose13 serves as a bridge between the robot and the workpiece with enoughforce to effectively lock these objects together. This samestabilization effect of the extended pressure foot plate 23 is utilizedduring actual drilling/milling operation of the end effector 10. Withthe pressure foot plate 23 and spindle nose 13 extended against theworkpiece, for example, laminations of material of the workpiece can beheld in contact with one another to obtain uniform results.

When the controller operating the end effector unit 10 has determinedthat the unit is located within acceptable limits through operation ofthe micro positioner 45, the end effector is deployed to machine an areaof the workpiece. Ordinarily, the pressure foot plate 23 and spindlenose 13 are retracted during gross positioning of the end effector by arobot or other manipulating device. As previously indicated, thepressure bridge frame 19 and spindle nose 13 are extended or retractedby operation of the servomotor 31.

As suggested, applications of an end effector can benefit from orrequire a pressure foot that, through a spindle nose 13, for example,first engages the work before a tool such as a drill bit is deployed.Moreover, it can be desirable to automatically remove a spindle nose orother extension of a pressure foot from an end effector when itsfunction is not required, when automatic tool changeover requiresremoval of the spindle nose, and/or when a different spindle nose isneeded.

An automatic tool changer 51 of special construction disposed betweenthe spindle nose 13 and the pressure foot plate 23 enables theseoperations to be performed automatically. FIG. 5 illustrates a masterside 52 and a tool side 53 of the tool changer 51 spread apart to showcertain details of these components. Each side 52, 53 is a generallyflat plate with a triangular outer profile and a large central bore 56,the latter preferably being sufficiently large to fit around the spindleand housing 46. A plurality of three ball locks 54 are fixed on an outerradial face of the master side 52 symmetrically disposed around the bore56. Each ball lock 54, as shown schematically in cross-section in FIG.6, has a cylindrical body carrying a set of radially movable balls 57.The balls 57 are held in radially outward positions by air pressureintroduced into a chamber 58 on an inner face of a piston 59 and arereleased when air pressure is introduced into the chamber 58 at an outerface of the piston 59. The chambers 58 of the ball locks 54 on one sideof their respective pistons 59 are interconnected, and on opposite sidesof the respective pistons are similarly interconnected. Pressurized airis admitted to one or the other sides of the pistons 59 under thecontrol of the end effector unit controller. It will be seen that whenthe pistons 59 are moved outwardly, the balls 57 are caromed and heldradially outwardly. In their radially outward positions, the balls 57are received in internal grooves 61 in bores 62 that receive thecylindrical ball lock bodies 54. When the balls 57 are extended into theinternal grooves 61 in the tool side 53, the master and tool sides 52,53 are locked together. The master and tool sides 52, 53 when initiallybeing joined, are mutually aligned by two pins 63 projecting axiallyfrom a face of the master side 52. The pins 63 are received incomplementary holes 64 in the tool side 53. Male and female brackets 66on the periphery of the sides 52, 53 couple the vacuum tube 21 to thespindle nose 13. The spindle nose 13 is rigidly bolted to the tool side53 and the master side is rigidly bolted to the pressure foot plate 23.The large bore 56 of the master and tool sides 52, 53 enables the leadend of the end effector unit spindle housing 46 to extend through it.This enables the housing 46 to be positioned as close as practical tothe workpiece so that the spindle 12 and the quill (like that shown inFIG. 9) are supported with a minimum cantilever effect even when thequill is extended.

FIGS. 7-9 illustrate another end effector unit 70; parts that areidentical or have substantially the same function to those shown in theembodiment of FIGS. 1-6 are identified with the same numeral. A bolsterplate 71 is fixed to the spindle housing 46. Three cantilevered, axiallyoriented guide rods 72 extend rigidly from the front face of the bolsterplate 71. FIG. 8 diagrammatically illustrates the location of theseguide rods 72 relative to the spindle axis 15. A pressure foot plate 73has linear bearing units 74 that receive the guide rods 72 and enablethe plate 73 to translate in the axial direction away from and towardsthe bolster plate 71. Bolted to the pressure foot plate 73 is atransducer or load cell assembly 76 which comprises an adapter plate 75carrying a load cell plate 77. Three load cells 79, equally spacedangularly and radially about the axis 15, are mounted on the load cellplate 77. A pressure plate 78, a part of the load cell assembly 76,bears against the load cells 79. The master side 52 of a tool changer 24is bolted to the forward side of the pressure plate 78. The tool side 53of the tool changer 24 carries a spindle nose 13.

It will be understood that the plates 73, 75, 77 and 78 each have a boresized to slip over the quill end of the housing 46. The load cells 79are force transducers of, for example, of the Hall Effect type andmeasure axial force applied by the spindle nose 13. A servomotor 31,under control of the end effector controller, rotating a ball shaft in aball nut 33 moves the spindle nose 13 against a workpiece or retractsthe spindle nose. It will be understood that the end effector unit 70,like the end effector 10, is supported in an operating position on theend of a robot arm or other manipulating device. At the rear of the endeffector unit 70, a tool side 11 of an automatic tool changer is fixedto the unit. While not shown, a tool changer tool side for mountingeither end effector units 10 or 70 can be fixed to a side of the unitwhere the geometry of the workpiece relative to the manipulating deviceis benefited.

The array of load cells 79 detects the normality or perpendicularity ofthe spindle axis 15 to the surface of the workpiece by differentialforce or displacement readings. When the servomotor 31 presses thespindle nose 13 against the workpiece, one or two of the load cells 79will be compressed to a greater degree than two or one of the other loadcells where normality is absent. The load cell or load cells on theacute side of the angle made between the spindle axis 15 and a planetangent to a workpiece surface will experience greater compression. Theload cell signals are relayed to the robot or other machine controllerordinarily through connectors at the rear tool changer 11 to enable thecontroller to reposition the end effector 70 through robot movement sothat the spindle axis 15 is more nearly perpendicular to the workpiecesurface to be machined.

FIG. 9 is a longitudinal cross-sectional view of the end effector unit70. The quill 81 is driven axially forward or rearward by a ball nut 82threaded on a ball screw 83. The ball screw 83 is rotated by theservomotor 16 (FIG. 7) through a sheave 84 and belt 86. A spindleassembly 87 carrying an automatic tool clamp 88 is rotated by a driveshaft 89. The drive shaft 89 is driven by the servomotor 18 (FIG. 7)through a belt 91 and sheave 92. An external spline 93 on the driveshaft 89 mates with an internal spline 94 of the spindle assembly 87 toaccommodate axial movement of the spindle assembly with the quill 81relative to the drive shaft 89. The automatic tool clamp 88 can be acommercially available unit such as manufactured by HSK. The tool clamp89 is biased to a closed position by spring packs 95, 96 (FIG. 9B)operating on a draw bar 97 running along the axis 15. As explained morefully in aforementioned U.S. Pat. No. 7,547,169, the automatic toolclamp 88 is opened or released when the quill 81 is fully withdrawn intothe housing 46 and the forward end of the drive shaft 89 compresses thespring packs 95, 96. The rear end of the draw bar 97 is received in acounterbore 90 in the forward end of the drive shaft 89. Both the driveshaft 89 and draw bar 97 have central axially extending bores 98, 99that communicate with one another. Extension and retraction of the quill81 causes the rear or tail end of the draw bar 97 to telescope out of orinto the forward end of the drive shaft 89.

Referring to FIG. 9A, the rear end of the drive shaft 89 is fitted witha rotating union 101. The rotating union may be a commercially availableunit such as manufactured by Deublin Company headquartered in Waukegan,Ill. USA. Coolant or air can be admitted into a chamber 102 behind thestationary part of the rotating union to supply coolant through thedrive shaft and draw bar bores 98, 99 to the automatic tool clamp 88 andultimately to the drill or tool held in the tool clamp. A chamber 103drains coolant which may return from the bores 98, 99 when the unit 70is idling or otherwise inactive. A series of O-ring seals 104 aredisposed in the counterbore 90 in the forward end of the drive shaft 89for sealing on the exterior of the draw bar 97 to contain the coolant inthe bores 98, 99.

While the invention has been shown and described with respect toparticular embodiments thereof, this is for the purpose of illustrationrather than limitation, and other variations and modifications of thespecific embodiments herein shown and described will be apparent tothose skilled in the art all within the intended spirit and scope of theinvention. Accordingly, the patent is not to be limited in scope andeffect to the specific embodiments herein shown and described or in anyother way that is inconsistent with the extent to which the progress inthe art has been advanced by the invention.

1-11. (canceled)
 12. An end effector for drilling and/or millingcomprising a quill housing, a quill in the housing, a spindle rotatablysupported in the quill for rotation about an axis, the quill beingguided for axial reciprocation along the axis of the spindle, thespindle including an automatic tool clamp on an end thereof, a spindledrive shaft axially fixed and rotatably supported in the quill housing,a draw bar for opening and closing the automatic clamp, a rear end ofthe draw bar being telescoped in a forward end of the spindle driveshaft, the spindle drive shaft and the draw bar having central passagesalong their respective lengths and in communication with each other tosupply coolant from a rear end of the spindle drive shaft to theautomatic tool clamp, and a seal, disposed between an inside of thedrive shaft and an exterior of the draw bar to resist coolant leakagethrough telescoped areas of the spindle drive shaft and draw bar.